Does interspecific hybridization influence evolutionary rates? An experimental study of laboratory adaptation in hybrids between Drosophila serrata and Drosophila birchii.

The low initial fitness of progeny from interspecific crosses in animals and the rarity of interspecific hybridization in natural environments have led to a debate about the evolutionary importance of this phenomenon. Here we directly assess the effects of hybridization between Drosophila serrata and Drosophila birchii on evolutionary rates. We looked at the effects on laboratory adaptation over 30 generations in two laboratory environments, one of which involved nutrition and temperature stress. Laboratory adaptation occurred over time in both environments as reflected by a marked change in viability. However, whilst hybrid lines at no stage performed poorly relative to parental lines, their rate of adaptation never exceeded that of the parentals. Thus, there was no evidence that hybridization increased evolutionary rates. Instead, hybrid lines converged phenotypically with one of the parental species.